1. Field of the Invention
The present invention relates to a method and apparatus for forming tees in tubing or other metal products. The apparatus and method of this type can work the metal surrounding an opening in the wall of a tube or a plate to flare the edge of the metal surrounding the opening outwardly and increase the size of the opening until an outwardly projecting collar or neck is formed around the enlarged opening. This collar can form a support to which a branch tube can be affixed by welding, for example.
2. Related Background Art
Many methods of manufacturing a branch pipe joint or tee are known. For example, Japanese Laid-Open Patent Application No. 59-33036 discloses forming a branch pipe joint of large diameter by first forming an elliptical hole in the body of a short pipe, fixing the pipe in a forming die having a through-hole, and positioning a receiving stand in the pipe. A small ball is positioned on the receiving stand adjacent the elliptical hole and it is forced through both the elliptical hole in the pipe and the through-hole in the die by pressing with a cam rod. The small ball is replaced with a larger ball and a secondary stage is performed using a second forming die having a larger through-hole. The larger ball is forced through the enlarged hole of the pipe and the larger through-hole of the second die using a second receiving stand and a second cam rod. Thus, a large diameter branch pipe joint is obtained.
Japanese Laid-Open Patent Application No. 55-122627 also relates to a method of producing a branching pipe. First, an elliptical hole is formed in a portion of a base pipe and the periphery of the hole is heated. A thickness-increasing die is forcibly inserted into the elliptical hole and then a forming die is pulled from inside of the elliptical hole to the outside. Thus, a branch pipe is obtained.
U.S. Pat. No. 1,792,928 relates to a method of forming a pipe outlet in a steel header pipe. A hole of an elliptical shape is punched or drilled in the wall of the header and is then enlarged by expanding the metal with an extrusion press.
U.S. Pat. No. 1,911,653 discloses a method of making pipe tees from a blank of wrought metal tubing. The ends of the blank are cut on transverse planes. A circular opening is formed in the blank, which is heated to a suitable flowing temperature and then placed in a cavity defined by upper and lower holding dies. A mandrel having a cylindrical recess, which receives a cylindrical former, is placed in the blank. When the blank is disposed upon the mandrel, the opening is concentric with the recess so that a pull rod can be secured to the former by a bayonet connection. Pressure dies are slidably mounted upon the mandrels and are forced toward each other by hydraulic pressure, for example. The pressure applying dies are then moved inwardly so as to displace and redistribute the metal at the upper portion of the blank. The metal of the blank may then flow outwardly through an opening of an upper holding die. The outward flow is guided by the cylindrical former, which is raised. Inward movement of the dies continues until the ends of the blank are normal to the longitudinal axis thereof. Thus, the pipe tee is formed.
U.S. Pat. No. 2,507,859 relates to a method of making pipe fittings in which a hole is cut into a tubular blank. The blank is then heated and positioned between upper and lower dies of a press. A pullout plug includes a round body, a neck and a head, which is passed from the interior of the blank through the hole. The head of the plug is inserted into a socket affixed to a supporting rod. As the upper die descends, the metal of the blank is drawn over the body of the plug to form the tee.
All of the processes just described use a pilot hole of either an elliptical or circular shape. However, elliptical pilot holes are difficult to machine. An inordinate amount of force is required to pass a forming member through elliptical and circular shaped pilot holes, which can give rise to tearing of the material. Further, such methods, especially when used in a hot-forming process, can give rise to uneven radiuses in the turn from the main bore to the tee. Moreover, these methods give rise to a thinning of the wall of the tubing in the tee portion. Thus, the coupling may be weakened in these areas and may not be satisfactory for high pressure applications.